Structural, microstructural, and mechanical characterization of borosilicate glass-ceramic composites reinforced with alumina, spinel, and zirconia — fabricated, heat-treated, and tested as part of a final-year undergraduate thesis in Materials/Aerospace Engineering.
Glass-ceramics are a compelling class of structural materials for aerospace and high-temperature applications: lighter than metals, thermally stable, corrosion-resistant, and capable of being engineered through controlled crystallization. This thesis investigates how composition and heat-treatment schedules determine microstructure and how microstructure drives mechanical performance.
- Design borosilicate-base glass compositions reinforced with Al₂O₃, spinel (MgAl₂O₄), and ZrO₂
- Determine nucleation and crystallization temperatures via Differential Thermal Analysis (DTA)
- Fabricate glass-ceramic composites through melt-casting and controlled heat treatment
- Characterize microstructure: optical microscopy, SEM, XRD, EDS
- Measure mechanical properties: three-point flexural strength, Vickers hardness
- Correlate microstructural features (crystallinity, porosity, crystal morphology) to failure mechanisms
| Stage | Process | Parameters |
|---|---|---|
| Batch preparation | Weigh + mix silica, boric acid, alumina, MgO, CaO | Target crystalline phase: anorthite, cordierite |
| Melting | Platinum crucible, electric furnace | 1350–1500°C |
| Casting & annealing | Steel molds, stress relief | 500–550°C, 2h |
| DTA | Identify nucleation/crystallization peaks | Heating rate: 10°C/min |
| Heat treatment | Two-stage nucleation + crystallization | 600–700°C (nucleation), 900–1100°C (crystallization) |
| Sample prep | Diamond saw cut, polished rectangular bars | 60×10×4 mm for UTM, small sections for SEM |
| Microstructural characterization | XRD, SEM, EDS | Phase identification, crystallinity, composition |
| Mechanical testing | Universal Testing Machine (UTM), Vickers hardness | 3-point bend, 40mm span; 1 kg load |
| Property | Parent Glass | Partially Crystallized | Well-Crystallized |
|---|---|---|---|
| Flexural strength | ~45 MPa | ~80 MPa | ~160 MPa |
| Vickers hardness | ~5 GPa | ~6.2 GPa | ~7.1 GPa |
| Dominant phases | Amorphous | Anorthite + residual glass | Anorthite + cordierite + ZrO₂ |
- Phase formation: XRD confirmed anorthite and cordierite as primary crystalline phases; ZrO₂/spinel secondary phases increased with respective additive concentrations
- Microstructure: SEM showed fine dendritic crystals (1–5 μm) in residual glass matrix; higher Al₂O₃ promoted elongated crystal growth and crack-deflection paths
- Failure mechanism: Mixed transgranular/intergranular fracture; crack branching at crystal-glass interfaces increased energy absorption and fracture toughness
- Heat treatment effect: Longer crystallization hold times reduced residual glass content and porosity, systematically increasing both strength and hardness
Undergraduate-Thesis/
├── reports/
│ ├── Batch7_Thesis_Report.docx # Full thesis report
│ └── Major_Project_Phase2_Review.pdf # Phase 2 progress review
├── slides/
│ └── Thesis_Presentation.pptx # Final presentation
├── figures/
│ └── thesis_figures.zip # SEM micrographs, XRD patterns, stress-strain curves
└── README.md
This work directly addresses skills relevant to materials and composites engineering roles:
- Materials processing — glass melting, casting, controlled heat treatment scheduling
- Microstructural characterization — SEM, XRD, EDS, optical microscopy
- Mechanical testing — UTM three-point bending, Vickers hardness, fractography
- Structure-property relationships — quantified how crystallinity and phase composition drive strength
- Data analysis — statistical analysis of flexural strength (mean, std dev across specimens)
This thesis was submitted as the final capstone of a B.Tech in Aerospace/Materials Engineering. The research was conducted in the Materials Science laboratory using department equipment and supervised by faculty in the Department of Aerospace Engineering.
- Kingery, W.D., Bowen, H.K., & Uhlmann, D.R. (1976). Introduction to Ceramics, 2nd ed. Wiley.
- Strnad, Z. (1986). Glass-Ceramic Materials. Elsevier.
- ASTM C1161: Standard Test Method for Flexural Strength of Advanced Ceramics.
- ASTM C1327: Standard Test Method for Vickers Indentation Hardness of Advanced Ceramics.